Wool treatment



XR 3s250s587 3,250,587 Patented May 10, 1966 3,250,587 WOOL TREATMENT Gerald T. Gallagher and Harry N. Tobler, Trenton, N.J.,

assignors to FMC Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 10, 1363, Ser. No. 329,383 Claims. (Cl. 8107) This invention relates to the bleaching of wool, and particularly to a process which bleaches wool to a high brightness in an unusually short time and without substantially degrading it.

Wool as it is obtained from the animal and following scouring, mechanical processing, e.g. carding, and other normal cleansing operations, is of a yellowish cast. For most applications it is necessary that it be bleached regardless of whether it is to be used in its undyed state or it is to be dyed.

Bleaching processes employed heretofore with wool have had one over-riding, common problem, namely achievement of effective bleaching without excessive degradation of the proteinaceous fibers which comprise the wool. In order to avoid degradation of the wool by the bleaching agents, which normally are strongly acting chemical reagents such as alkaline hydrogen peroxide and the like, it has been necessary to carry out the bleaching with concentrations of the reagents, and at temperatures, which require excessively long bleaching times. Thus the normal bleaching process which employs aqueous hydrogen peroxide is carried out at a temperature up to on the order of 120-135 F. and requires treatment over a period of at least about 1 to 3 hours. As indicated, when it is attempted to speed up this bleaching reaction by raising either the temperature or the concentration of the chem icals, excessive degradation of the wool, as evidenced by alkali solubility occurs. This characteristic is a measure of the chemical breakdown of the wool molecule, and is set forth in ASTM Test Method D1283-5 3T. Even under the most carefully applied and selected conditions, however, an objectionable degree of degradation has occurred.

It therefore has been desired, and is the principal object of this invention, to provide a method of bleaching wool which both achieves a high degree of brightness and does so in a sufiiciently short time to permit continuous operation in simple equipment, yet does not adversely affect the wool.

It has now been found that wool can be bleached rapidly, essentially without degradation, by a process which achieves excellent brightnesses, by saturating the wool with a first aqueous solution containing about 1 to and preferably 3 to 5%, of an alkali bisulfite to provide 50 to 150% by weight of this first solution on the wool, immersing the saturated wool for from about 5 seconds up to about 10 minutes in a second aqueous solution containing about .001 to 10%, and preferably .01 to 1.0%, by weight of an alkali borohydride and used in an amount to provide in contact with the wool about 0.05 to 7%, and preferably 0.2 to 2%, by weight of the alkali borohydride based on the weight of the wool being treated, during the immersion in the borohydride solution providing a pH of 1 to 8, and preferably of 5 to 7, in the immediate environment of the wool, withdrawing the treated wool from the second solution and within 10 minutes from commencement of the borohydride treatment, removing the borohydride therefrom either by washing it with water or by heating it to a temperature of about 110 to 180 F., and preferably 130 to 160 F., for about 10 to 30 minutes to decompose the borohydride therein. Preferably the wool is treated mechanically to reduce the amount of second solution carried on it prior to the heating, for the obvious reason that this reduces the amount of heat required. Removal of borohydride is essential to avoid discoloration of the treated wool, which occurs if the borohydride is exposed to oxygen in the atmosphere or in water after the wool has been permitted to remain in contact with the borohydride and the bisulfite compound for more than 10 minutes before such exposure to oxygen.

The bleaching steps of this process can be carried out in as little as 10 seconds, and provide excellently bleached wools having brightnesses fully equivalent to those produced by the best prior art processes. It may be theorized that the bisulfite and borohydride react to form sodium hydrosulfite which is known as a reducing bleaching agent. However, the mechanism of bleaching by the present process cannot be this straightforward. These two reagents have been employed previously in aqueous solution in processes in which they efiect a chemical change in proteinaceous fibers, for example in the dekinking or setting of hair. The present process, on. the other hand, is of particular value largely because it operates without any substantial chemical change in, that is degradation of, the proteinaceous wool fiber. Furthermore, attempts made after discovery of the present process to achieve by addition of hydrosulfite the degree of brightening of wool provided by the present process have been unsuccessful, and also the browning of the wool experienced in the present process when the wool is not freed of borohydride promptly is not encountered after treatment with hydrosulfite. Likewise, and most importantly, the bleaching which is achieved by the hydrosulfite is not provided in anywhere near the short times in which the present twostep process operates. Accordingly, the mechanism by which this process operates and the reasons for its advantages are not susceptible to ready explanation.

The wool treated by the process of this invention is in the form of fibers, tow, yarn or fabric. Normally it is scoured in a conventional manner, for example in an aqueous scouring bath containing a nonionie wetting agent such as Triton X-100, an isooctylphenyl polyethoxy ethanol containing about 9 moles of ethylene oxide per mole of isooctylphenol, prior to treatment with the bisulfite. The scour is not necessary, but has been found to provide for uniform bleaching by removing natural impurities such as oils, dirt and the like, and also to avoid wasteful decomposition of the bleaching agent by some of the impurities which are removed by the scour.

Following the scour, the wool is saturated with an aqueous solution of an alkali bisulfite, namely 'a bisulfite of an alkali metal, an alkaline earth metal or ammonium. The particularly preferred bisulfites are the sodium, potassium, magnesium and ammonium bisulfites. The bisulfite may be formed in the aqueous solution from other sulfuroxy compounds which in aqueous solution convert to the bisulfite. Thus, for example, the metabisulfites and sulfites, as well as sulfur dioxide in the presence of water and alkali ions, convert to the alkali bisulfite at the herein pH of 1 to 8 to which the bisulfite solution is brought for reaction with the borohydride on the wool.

The bisulfite is employed in aqueous solution at a concentration of about 1 to 10%, and preferably 3 to 5%, by weight. Normally, the saturation or impregnation of the wool with the first aqueous solution, which contains the bisulfite, is carried out by immersing the wool in the solution, removing it and expressing all but 50 to of the solution on the weight of the wool.

The pH of the bisulfite solution is such that it creates in the environment of the wool as the latter is present in the borohydride solution, a pH of 1 to 8, and preferably of 5 to 7. In an environment having a pH greater than about 8 the bisulfite-borohydride system is substantially less effective as a bleach than it is at a pH below 8.

The bisulfite solution accordingly is used at a pH below 8, and preferably at a pH which is substantially acid in order to provide local acidification of the borohydride solution, which normally is maintained at a pH of above about 8 for stability reasons. Where necessary the pH of the bisulfite solution is adjusted with an acid, for example a mineral acid such as sulfuric acid or an organic acid such as a lower aliphatic acid exemplified by acetic acid, a sulfonic acid or the like.

The alkali borohydride employed is an alkali metal or alkaline earth metal borohydride, preferably the sodium, potassium, lithium or magnesium borohydride. The alkali borohydride is a solid and is stable in this form. When it is introduced into the aqueous solution employed in the second step of the process of this invention, its pH is normally but not necessarily maintained above neutral to avoid decomposition of the borohydride. This agent is employed in aqueous solution at a concentration of about 0.001 to and preferably of 0.01 to 1%, by weight. The solution is employed in an amount to make available for contact with the wool about 0.05 to 7%, and preferably 0.2 to 2%, by weight of the borohydride on the weight of the wool. It is apparent that the lower concentration borohydride solutions, and the lower wool-contacting amounts of borohydride solution, are used with wool containing the lower amounts of bisulfite, and the larger amounts of borohydride with the larger amounts of bisulfite.

The expression available for contact with the wool as used above with reference to the amount of solution takes into account the fact that when the bisulfite-saturated wool is immersed in the borohydride solution, only that borohydride in contact with the wool, and therefore with the bisulfite carried thereon, is available for reaction. The amount of borohydride contacting the wool may be varied by agitation of the solution, for example by moving the wool through the solution, but in the absence of such agitation the amount of borohydride contained in a given weight of solution about equal to the weight of the wool can be considered to contact the wool and bisulfite. With this in mind, one part by Weight of borohydride should be made available for contact with wool containing about 2.5 to 9 parts by weight of bisulfite.

The wool is permitted to remain in contact with the borohydride solution for no more than 10 minutes, whereupon it either is heated to about 110 to 180 F., and preferably 130 to 160 F., for about 10 to 30 minutes, or it is washed with water, preferably with the aid of commonly used wool-washing detergents such as Triton X-100. This washing or heating step is carried out to destroy residual borohydride on the wool; if this agent is not destroyed in this time, when the wool is contacted with air, even that in water, the wool darkens. Where the heating step is used it is preferred to wash residual chemicals from the wool with water. Following washing, the wool can be dried in any normal way, for example in an oven at about 110 to 180 F.

The process of this invention desirably is carried out at ambient temperatures, that is, in the range of temperatures of normal processing water, about 60 to 80 F. However, it is possible to carry the process out effectively at temperatures as low as about 40 to 50 F. or as high as 230 F., temperature not being critical in the process because the time-temperature relationship usually encountered with bleaching agents such as hydrogen peroxide is not found to be a serious factor in this process. Accordingly, it is desirable to operate the process without either cooling or heating the solutions; this has. the added advantage of not resulting in accelerated decomposition of borohydride as sometimes occurs upon the application of heat.

The process of this invention is particularly suited to continuous operation because of the short times required for the treatments in the baths involved. Furthermore, no complicated equipment or temperature controls are necessary for operation of this process and the bleaching agents employed are quite stable and the baths may be employed continuously with simple replenishment of the reactants as necessary. It is possible, however, to carry the process out batchwise, and this is done where only a few pieces are to be bleached, or equipment is not available which is suitable for continuous processing.

The following examples are presented by way of illustration of the process of this invention and are not to be considered as limiting the scope thereof in any way. All percentages referred to in the examples are percentages by weight. Reflectance values were determined on a Hunterlab Reflectometer Model D-40, employing a blue filter. The wool samples employed were scoured before treatment for 30 minutes at F. in a 0.2% aqueous solution of Triton X-l00, followed by a water-wash and drying at 150 F.

EXAMPLE 1 A scoured light-weight apparel-grade wool fabric having a reflectance of 37.3% was impregnated in a 5% aqueous solution of sodium bisulfite having a pH of 4.8. It was then squeezed to leave in the wool an amount of solution equal to the weight of the dry wool, and the saturated wool was placed immediately into a solution containing 0.1% of sodium carbonate and 0.01% of sodium borohydride maintained at 80 F. and having a pH of 9.2. The solution was permitted to remain in this bath for 15 seconds during which time the pH of the solution in the immediate environment of the wool was between 5 and 7.0. The fabric was then removed, washed with water and dried at 160 F. for 15 minutes. The reflectance following bleaching was 48.7%.

By way of comparison, a 3-hour bleach with a 0.3% solution of hydrogen peroxide containing also 0.17% of ammonium hydroxide, and 0.17% of tetrasodium pyrophosphate carried out at F. provided a reflectance in the wool of 46.2%.

EXAMPLE 2 A sample of wool fabric from the same batch as that employed in Example 1 was bleached under the same conditions but employing an aqueous solution containing 0.1% of sodium borohydride and having a pH of 9.3 in place of the 0.01% solution used in Example 1. The reflectance of the bleached wool fabric in this case was 50.4%.

EXAMPLE 3 A sample of wool fabric taken from the same batch as that used in Example 1 was immersed in an aqueous solution containing 5% of sodium bisulfite and having a pH of 4.8, and maintained at 120 F., for 15 minutes. The fabric was then removed from this bath and squeezed to provide a retained weight of solution on the fabric equal to the weight of the fabric. The saturated fabric was then immersed directly in an aqueous solution containing 0.1% of sodium carbonate and 0.1% of sodium borohydride and having a pH of 9.3, for 15 seconds. The pH of the borohydride solution adjacent the wool was about 5 to 7.0, and the temperature of the solution was 70 F. The fabric was then removed from the bath and cut into two equal portions, one portion was washed with water and dried and the other was squeezed to 100% saturation and then dried at to F. for 15 minutes without washing. The portion of the sample which was heated and dried without Washing had a reflectance of 55.7%. The portion which was washed had a reflectance of 54.2%.

EXAMPLE 4 A sample of wool fabric, a coarse, heavy blanket grade normally diflicult to bleach, was immersed for 15 seconds in an aqueous solution containing 5% of sodium bisulfite maintained at 100 F. and having a pH of 4.8. The fabric was then removed from this solution and squeezed to provide on the fabric a weight of solution equal to the TABLE Whiteness Alkali Time of NaBH Treatment (Min) (percent Solubility Reflectance) These results were compared with an immersion bleach of wool fabric in a hydrogen peroxide bleach. The hydrogen peroxide bleach method consisted of treating the wool fabric for 3 hours at 130 F. with a solution containing 0.2% hydrogen peroxide, 0.17% ammonium hydroxide and 0.17% tetrasodium pyrophosphate. After this treatment the wool fabric was washed with warm water and dried at 150 F. The results of the hydrogen peroxide bleach were a reflectance of 46.1% and an alkali solubility of 19.8%.

EXAMPLE 5 A sample of yellowish wool stock after scouring by the above process was saturated to the extent of 100% by weight of the stock with a 5% aqueous solution of sodium bisulfite having a pH of 4.8. The stock was then immersed for 60 seconds in an aqueous solution maintained at 125 F. and containing 0.1% sodium carbonate and 0.1% sodium borohydride, and having a pH of 9.3. The pH in the area of the wool was between 5 to 7.0. The stock was removed from this solution and squeezed so as to retain a weight of the solution equal to the weight of the wool, and placed in a forced air dryer maintained at 150 to 160 F. for 15 minutes. The bleached wool stock had an excellent degree of whiteness compared with the stock before bleaching.

EXAMPLE 6 Scoured wool yarn was immersed in an aqueous solution held at 120 F. and containing 5% of sodium bisulfite for 15 minutes. The pH of the solution was 4.8. The yarn was then removed from the solution and squeezed to provide 150% of the weight of the yarn of solution in the yarn. It was then immersed for 60 seconds in an aqueous solution containing 0.1% sodium carbonate and 0.1% sodium borohydride having a pH of 9.3. The yarn was then removed from the solution, washed with water and dried at 160 -F. The resulting bleached yarn had a 6 brightness better than that obtained with a standard 3- hour immersion bleach with 0.2% of hydrogen peroxide described in the comparative portion of Example 4.

EXAMPLE 7 Sodium hydrosulfite bleach for comparison A sample of the wool fabric bleached by the procedure of Examples 1 through 3 was immersed in a bath containing 2% of sodium hydrosulfite maintained at F. for 15 minutes. The fabric was then removed and washed with warm water and dried at F. The reflectance of the resulting bleached fabric was 42.9%

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise than as specifically described and exemplified herein.

We claim:

1. A method of bleaching wool, in which said wool is saturated with a first aqueous solution containing 1 to 10% by weight of an alkali bisulfite, the saturated wool is contacted for 5 seconds to 10 minutes with a second aqueous solution containing 0.001 to 10% of an alkali borohydride and used in an amount to provide in contact with said saturated wool 0.05 to 7% of said alkali borohydride on the weight of the wool, providing a pH of 1 to -8 in the immediate environment of the wool in said second aqueous solution, withdrawing the treated wool from said second aqueous solution within 10 minutes from the time it is immersed therein, and removing the borohydride from said treated wool.

2. A method according to claim 1 in which the first aqueous solution contains 3 to 5% by weight of an alkali bisulfite, the second aqueous solution contains 0.01 to 1% by weight of an alkali borohydride and is used in an amount to provide in contact with said saturated wool 0.02 to 2% by weight of the alkali borohydride, and a pH of 5 to 7 is provided in the immediate environment of the wool.

3. A method according to claim 1 in which the alkali bisulfite is sodium bisulfite and the alkali borohydride is sodium borohydride.

4. A method according to claim 1 in which the borohydride is removed from the treated wool by Washing said treated wool with water.

5. A method according to claim 1 in which the borohydride is removed from the treated wool by heating said treated wool at a temperature of 110 to F.

No references cited.

D. TRAVIS BROWN, Primary Examiner.

NORMAN G. TORCHIN, Examiner.

J. H. RAUBITSCHEK, Assistant Examiner. 

1. A METHOD OF BLEACHING WOOL, IN WHICH SAID WOOL IS SATURATED WITH A FIRST AQUEOUS SOLUTION CONTAINING 1 TO 10% BY WEIGHT OF AN ALKALI BISULFITE, THE SATURATED WOOL IS CONTACTED FOR 5 SECONDS TO 10 MINUTES WITH A SECOND AQUEOUS SOLUTION CONTAINING 0.001 TO 10% OF AN ALKALI BOROHYDRIDE AND USED IN AN AMOUNT TO PROVIDE IN CONTACT WITH SAID SATURATED WOOL 0.05 TO 7% OF SAID ALKALI BOROHYDRIDE ON THE WEIGHT OF THE WOOL, PROVIDING A PH OF 1 TO 8 IN THE IMMEDIATE ENVIRONMENT OF THE WOOL IN SAID SECOND AQUEOUS SOLUTION, WITHDRAWING THE TREATED WOOL FROM SAID SECOND AQUEOUS SOLUTION WITHIN 10 MINUTES FROM THE TIME IT IS IMMERSED THEREIN, AND REMOVING THE BOROHYDRIDE FROM SAID TREATED WOOL. 